Processes and devices for processing organic substances of low economic value which represents their limited utilisation are known, in particular in the field of crude oil processing. Recently, such processes find their application also in utilising, waste as a raw material source.
To the most efficient ways of utilising crude oil heavy fractions belong the decomposition processes which make use of fluidization. The most widespread fluid process for conversion heavy hydrocarbon fractions is the fluidised catalytic cracking process.
Fluidization is defined in technical practice as a state, in which solid particles are in the state of lift by a fluid (gas, liquid), streaming against the field of mass force (gravity), and such a system behaves on the outside like a liquid (suspension). The fluid layer has exceptional properties which are widely utilised in physical and chemical processes . . . . "Intensive motion of particles in the layer and stirring the layer account for high heat and matter transfer and quick balancing of temperature and concentration differences."--V. Mika: Zaklady chemickeho inzenyrstvi (Principles of Chemical Engineering), SNTL/ALFA 1981. The key to the exceptional properties of the fluid layer, utilised in chemical processes, consists in intensive stirring of solid particles by the fluidizing medium.
The problem of elimination of non-uniformities forming in the fluidizing bed is solved in the patent JA-A-05277354, where the fluidizing bed is formed by the fluidizing medium, in which bed particle agglomeration is prevented by using a stirrer in a circular reactor, wherein the motor driven stirrer rotates in the fluidizing bed. medium, in which bed particle agglomeration is prevented by using a stirrer in a circular reactor, wherein the motor driven stirrer rotates in the fluidizing bed.
JP-A-58223435 describes a fluidized bed reactor working with gas as the fluidizing medium in which a stirrer is located to prevent agglomeration of particles of the fluidized catalyst and deposition of the reaction products at the inner wall of the reactor.
Besides classical raw material sources for conversion processes in petrochemistry alternatives are intensively searched for waste utilisation, especially of waste plastic materials, to produce high-grade hydrocarbons.
EP-Al-0502618 describes conversion of plastics, in particular polyolefines, by gasifying them in a fluidizing bed of solid inert particles with a fluidizing gas at temperatures of 300.degree. C. to 690.degree. C.
EP-Al-0687692 describes thermal cracking of chlorinated plastics in a fluidizing bed, consisting of inert particles fluidized by a liquid, with subsequent absorption of chlorine compounds in a solid bed with calcium oxide.
FR-A-2613721 describes a process of synthetic waxes production by thermal decomposition of polyethylene and polypropylene at a temperature of 360.degree. C. to 500.degree. C., wherein the polyolefins are injected into a heated steel tube in the presence of water vapour.
U.S. Pat. No. 3,901,951 describes a method of waste polymer processing: In the first step the polymers are melted at a temperature below 250.degree. C., and in the next step the melt is injected into a thermal medium of fluidized solid particles at a temperature of 350.degree. C. to 550.degree. C. for pyrolysis. Gaseous products of the pyrolysis condense, whereby a mixture of liquid hydrocarbons is obtained. The solid particles may be fluidized using gases like air, nitrogen or water vapour, air being preferred.
Systems working with fluidization, especially chemical reactors, require very high capital expenditures. The lift of solid particles in a fluidized solid reactor is ensured by a streaming gas in most cases. The operations necessary for preparation of the fluidizing medium: compression or pumping of the liquid (gas), its heating, transport, distribution in the reactor, etc., as well as separation of the fluidizing medium from the reaction products, cooling, elimination of losses, etc., cause that the systems operating with the fluidizing bed are technically and, therefore, also economically (as concerns investments and operation) very demanding. The devices are complicated what is caused by the technically complicated maintenance of optimum reaction conditions. The fluidized solid reactors are economically justified only in the case of high performance which again makes an impact on the investment costs.
Moreover, fluidization is often accompanied with non-uniformity. Forming of non-uniformities, i.e. forming of bubbles, channels and pistons may cause breakdown of the processes running in the fluidizing bed, thus reducing the advantages of fluidization considerably.